Cathode-ray tube



Sept. H, 1951 J. M. CAGE 2,567,874

CATHODE RAY TUBE Filed Aug. 28, 1948 4 Sheets-Sheet 1 /Z INVENTOR E(/UIH/V/M (3 765 (g MWWMJ ATTORNEYS Sept. 11, 1951 J. M. CAGE CATHODE.RAY TUBE 4 Sheets-Sheet 2 Filed Aug. 28, 1948 i E Q M 4 m1 MM m d ATTO RN 5Y5 Sept. H, 1951 J. M. CAGE 2,567,374

CATHODE RAY TUBE Filed Aug. 28, 1948 4 Sheets-Sheet 5 INVENTORJae/Mlthe;

ATTORNEYS pi. H, H9511 I J. M. CAGE 2,567,874

CATHODE RAY TUBE Filed Aug. 28, 1948 4 Sheets-Sheet 4 INVENTOR my. C'ne:

ATTORNEY 5 Sept. 11, 1951 CATHODE-RAY TUBE John M. Cage, Montclair, N..l., assignor to Cage Projects, Ina, Union City,

of New Jersey N. J., a corporation Application August 28, 1948, SerialNo. 465,585

This invention relates to image reproducing tubes and more particularlyconcerns a new and improved image reproducing tube for television andother similar applications. One object of the invention is a new andimproved reproducing tube of the character set orth whereby increasedbrightness and definition and greatly improved stability and life areobtained.

Another object of the invention is an improved image reproducing tubeparticularly useful in the projection of televised and other images.

' Another object is a new and improved electron beam acceleratingstructure for reproducing tubes.

Another object is a new and improved method and means for shielding theelectron beam of cathode ray tubes and to prevent the accumulation offree electrons on the tube walls.

Still another object is an improved cathode ray tube for thereproduction of images.

Another object is an improved shield or screen structure for cathode raytubes.

Other objects of the invention will hereinafter appear.

For a better understanding of the invention reference is made to thefollowing description and accompanying drawings forming a part of thisapplication In the drawings- Fig. l is a somewhat diagrammatic viewillustrating one embodiment of the invention;

Fig. 2 is a cross-sectional view of Fig. 1 taken along the lines i, 2thereof Fig. 3 is another embodiment of the invention; h Fig. 4 is across-sectional view taken along the lines 6, d of Fig. 3;

Fig. 5 illustrates still another embodiment of the invention;

Fig. 6 is a cross-section of the embodiment shown in Fig. 5 along thelines 6,. 6 thereof;

Figs. 7 and 8 are cross-sectional views of still another embodiment ofthe invention;

Fig. 9 is a cross-section of a cathode ray tube embodying one form ofthe invention;

Figs. 10 and 11 illustrate still another form of the invention;

Figs. 12 and 13 illustrate still another form of the invention; and

Fig. 14 is a section along the line it, I l of Fig. 13.

In conventional image reproducing tubes the accumulation of freeelectrons on the tube walls is prevented by coating the inside of theglass hoot the portion of the tube where such shielding is desired. Forexample, in the conventional image reproducing tubes for television thiscoating in the form of colloidal graphite or carbon is applied to thecylindrical part of the tube at a point between the front end of theelectron gun and the image reproducing screen.

The use of such a colloidal graphite or carbon solution as a coating forthe conventional tubes is not entirely satisfactory. For instance, thehigher the accelerating voltages used the greater the tendency of thecarbon or graphite to contaminate the vacuum within the tube andmaterially impair the operation thereof. Moreover, the application ofthe shield directly to the glass tubing tends to limit the acceleratingvoltage which may be used due to the insulating problems, and thecoating of the interior of the tube is a comparatively expensiveoperation. By means of my invention I avoid these and other objectionsto the disadvantages of the conventional tube structures.

In Fig. 1 I have shown somewhat diagrammatically a tube whereincontaminating coatings are dispensed with whileat the same time the beamcan be adequately and completely shielded and the accumulation of freeelectrons prevented. This enables the use of very much higher voltageson image reproducing tubes and produces a tube that is more dependableand that will have a very much longer life. In the figure, it denotesthe cylindrical section of the glass envelope, and I? a portion of theconical'section thereof. In the lefthand end of the cylindrical sectionlit the filament and cathode structure are denoted by the numeral It,the control grid or grids are denoted by the numeral Iti following thecathode and the next successive element is the second or high voltageelectron beam accelerating anode iii. To shield the electron beam as itleaves the second anode it, I have provideda plurality of rod orwire-like members 2@ surrounding the beam and spaced from thecylindrical section it. These rod-like members it are substantiallyuniiormly spaced one from the other and are connected together at oneend by means of a suitable metallic ring 22 which also acts as themechanical support for the individual rods or wires it. This structurecan be supported centrally within the tube it by any suitable means andmay in turn also be arranged to support the second anode it. This may beadvisable under certain conditions wherein it is desired to maintainboth the shield and the second anode at the same high potential.

In cathode ray tubes embodying the magnetic deflection coils my new andimproved" shield for the cathode ray beain is particularly effectivesince the coils usually surround the tube at a point after the secondanode l8 and the magnetic fields must pass through the shield. With myshield I have been able to reduce both eddy and circulating currents toa minimum and by making the rod-like" members of a non-magnetic metallicmaterial I have found that I can obtain excellent beam controlcharacteristics of the tube with little or no undue load on thedeflectin coil. As a matter of fact I have found that my new andimproved shield has little or no effect on the power consumed by thesurrounding magnetic deflection and focusing coils. while at the sametime it effectively shields the cathode ray beam and prevents thecollectionof free electrons during the operation of the tube and willnot in any way contaminate the vacuum therein. If desired, the surfaceof the shield can be blackened and the tube coated on the outsidethereof to reduce reflection of light onto .the image reproducingscreen. 3

In Fig. *3 I have illustrated an embodiment of the invention wherein theshield or screen is formed integrally with the second anode element [8.In-this figure. .lfl denotes the cylindrical section of the tube and I2denotes the conical section. At the left of the tube is againillustrated the cathode it having a filament l4 therein, a control gridor first anode l6 and a suitable in-: sulating'support 2|and-insulating. rods 26 for supporting the elements I4 and IS in properalinement. The shield consists of a plurality of spaced metallic wires28 preferably of a nonmagnetic material such as Monel or the like,although under certain conditions magnetic materials would besatisfactory. These wires are curved. inwardly toward the second anodel8 and are fastened thereto by welding or other suitable means. Therighthand section of the wires 28 is curved outwardly as they pass thejunction between the cylindrical and conical sections "of the tubeenvelope. so that the end portions of the wires will not interfere withthe picture in any way. The second anode it together with the shieldingwires 28 are supported in proper position within the tube by an innercylinder 30 of insulating material having flanges 30' on each of itsends for fastening it in position within the tube It; Each of. the wires28 is curved outwardly from the second anode [8 to meet the innersurface of the glass sleeve 30, whereupon it extends longitudinallyalong the surface 30 to the end thereof and is then curved outwardly asindicated at 28'. To rigidly support the wires in their spaced position,each wire 28 may be embedded-in the glass sleeve 30 substantially asshown at 32 in Fig. 4. Surrounding the cylindrical tube part III arecoils 34 and 36 for focusing and deflecting the electron beam as itleaves the accelerating anode l8 through the orifice i8 therein.

The deflecting coil 6 generates two alternating magnetic fields so thatthe electron beam will scan the screen-in the tube in both horizontaland vertical directions. If a large body of metal or other conductingmaterial of low resistance is placed in the center of the coil, largecirculating and eddy currents will be induced therein. I have avoidedthe generation of these currents by shielding the beam with anelectrically conductive shield having a plurality of spacedwiresconnected at only one end so that circulating current arecompletely eliminated and eddy-currents are reduced to an insignificantamount. Moreover, I have actually found that by using a plurality ofspaced wiresin the manner illustrated a uniform electrostatic fieldis-produced about the beam to collect free electrons and there is noindication whatsoever in the resultant pic ture to indicate in any waythat the shielding has been accomplished in this manner.

Although I have illustrated "in Figs.=- 1-4 wire or rod-like metallicmembers spaced about the beam and extending longitudinally thereof, eachwire could 01' course be in the form of a helix, or the shield couldcomprise a screen formed by weaving individual strands of wire in such amanner as to prevent the generation of circulating currents that wouldplace an undesirable load on the deflecting coils. In Figs. 7 and 8 Ihave shown a modification oi the structure illustrated able process andthen removing the sliver from the surfaces 40 between the grooves 38.With the silver deposited inthe grooves 38, the second anode l8 having aplurality of short outwardly extending spring-like fingers 42 would then.be placed in the sleeve with each-finger resting in one of the grooves3!! to contact the silver strips and connect them together.

An alternative arrangement is shown in Figs. 5 and 6 wherein I haveillustrated the glass sleeve 30' fastened in the tube part It aspreviously described in connection with the sleeve. 30 in Fig.

I 3. In this adaptation the shield comprises an extremely thin layer 46of platinum bright, palladium or other metallic coating having aresistance of preferably at least -200 ohmsper square inch. The materialof which the surface 48 is formed should be of a non-evaporatablematerial when used under normal voltages and temperatures experienced inthe operation of cathode ray tubes so that it will not contaminate thetube inany way. w

By embodying the insulating sleeve structure within the cylindrical tubepart 'III as illustrated in this and other figures, I am able to apply.extremely high voltages-to the tube without the danger of puncturing thetube should a relatively low potential or grounded surface be broughtinto close proximity with the outer part of the tube envelope. Thisstructure also effectively shields the tube beam and will not result incontamination of the tube with the application of high voltages thereto.

Moreover, with the structure I have been able to applyaccelerating'potentials to the tube of the order of 50,000 to 75,000volts and even higher without damaging the envelope 10, 12 in any way.

In the embodiment shown in Fig. 5 the second anode l8 can be supportedby the glass sleeve 30' in any suitable manner as by a number; ofsprings 44 fastened to the anode and extending outwardly to bear againstthe metallized and non-evaporatable surface 46 of the inside of thesleeve 30. v

Fig. 6 is a cross-sectional view of the form of the invention of Fig. 5and illustrates the spacing obtained between the outer surface of thetube envelope part III and the inner shielding layer 46. The gap betweenthe concentric cyiin;

drical portions 35 and I is of course evacuated along with theevacuation of the tube as a whole and provides a high degree ofinsulation to prevent arc-over and irreparable damage to the tube.

Another important advantage of the structures heretofore described isrealized particularly in humid weather. Normally a projection type raytube, for instance. is completely enclosed in a cabinet and itstemperature is therefore at a fairly low value with reference to theambient temperature during times when the set is not operating. Undersuch conditions a thin film of moisture may condense on the outersurface of the tube and in the presence of dirt and dust which usuallyalso settles on the tube a fairly good conductive layer to ground willbe formed. If the potential on the shield, which is conventionallydisposed on the inner wall of the tube part it. exceeds the normaldielectric strength of the glass, the tube wall will be punctured. Thisis a very definite limitation on the capacity of cathode ray tubes. Withmy invention, however, I can materially increase the potential to beapplied to the shield without danger of breakdown and I can moreoveravoid contamination of the tube by reason of the particular character ofthe shielding structure and, in addition, eliminate for all practicalpurposes circulating and eddy currents which produce an undue load onthe deflection coil.

In Fig. 9 I have illustrated an alternate embodiment of the invention.This embodiment is somewhat similar to the embodiment shown in Fig. 3 inthat a plurality of individual wires or rods it are fastened at one endto the second anode i8 and extend longitudinally of the tube. In thisembodiment an internal tubular glass sleeve 50 is supported at thelefthand end at the base it! of the tube Ill, and is provided at itsother end with a slightly flanged section 52 which curves outwardly tocontact the inner surface of the cylindrical tube part It at the pointwhere it begins to taper outwardly to form the conical or flared sectionit. In this embodiment the wires or rods terminate within the flangedsection if and are flared outwardly so that the ends of the wires willnot interfere with the electron beam at the edges of the picture to beformed on the screen of the tube. The wires 2t may be embedded in theglass tube 50 as previously set forth. or they may just rest against theinner surface thereof and be held in place by frictional contact. Itwould also be possible to use a structure such as shown, for instance,in Fig. '7 wherein the small grooves as may be used to retain the wiresft in properly spaced alinement about the inner surface thereof.

Still another method of forming my new and improved tube structure whichI have found to be particularly satisfactory is illustrated in Figs. 10and 11 wherein the cathode ray tube is formed of a cylindrical sectionwe. as previously described, which terminates in a flared section ifcurving outwardly to form a bell-like part which is closed at its largerend to provide a surface for receiving and holding the fluorescentscreen on which the picture is formed. In this embodiment a circularglass sleeve M1 is flared outwardly either side of a point substantiallyin line with the front or righthand end of the anode it. The wires aswhich are uniformly spaced about the electron beam and act to shield theelectron beam, as previously described, are each fastened at their innerends to the anode it and curved outwardly therefrom to form, in theirposition of rest, a cone with the base part being three or four times Iend the diameter of the of the anode I8 is provided with a flange I!surrounding the anode and through which the several wires 56 are passed.The flange 58. however, tion of the tube 54 so that when the anode I8 isinserted from the lefthand end the flange 58 will contact the internalwall of the tube 54 to limit any further forward movement. Since thewires 56' are flared outwardly in their position of rest. they will,upon being compressed for insertion into the tube 54, expand tofrictionally contact the inner wall of the front portion 54' of theglass tubular part 54 and tend in effect to pull the flange 58 forwardlyto securely engage it with the internal wall of the sleeve 54. Thisstructure provides a completely self-supporting structure for the secondanode together with the shielding wires 56. The tube 54 may be held inposition within the tube envelope part It! either by welding the sleeve54 in position in the tube In, or by providing suitable flanges orprojections on the inside of the tube part ill to limit the longitudinalmovement of the inner sleeve or tube 5%.

This particular structure therefore provides a simple and efiectivemethod for holding the second anode and shield in place and providing arelatively long leakage path inside the tube to prevent arc-over to theother controlled electrodes as well as to prevent breakdown through thetube walls due to the close proximity of a ground to the tube wall orthe formation of a conductive path along the wall to a grounded point onthe tube of the apparatus with which it may be associated.

With this new and improved gun structure and more particularly the newand improved.

shield and mounting therefor, a more dependable and stable tube isprovided that is capable of producing a very much improved picture.

In each of the previous embodiments I have illustrated the shield asterminating at just inside the flange section I: of the tube and curvedoutwardly slightly so that it will not interfere with the normalexcursions of the beam within the tube. This structure, however,particularly provides, in another aspect, other important advantageswhich result in further improvement in the cathode ray tube.

In conventional tubes to my knowledge the fluorescent screen is normallydisposed on the closed end i2 of the flared section l2 of the tube andbecause of certain structural requirements'the front end of the tube i2must necessarily be curved outwardly slightly. The formation of apicture on this curved surface produces some degree of distortiontogether with the fact that dirt, finger marks and other smudges on theouter part of the tube front i2 will tend to impair or obliterate theprojected image to some nt. This is particularly noticeable inprojection, since both the inner and outer surfaces of the front wallare substantially in focus.

' Moreover, since the screen is not flat it is sometimes necessarytostop the lens down to some extent to increase the depth of focus so thatall parts of the picture will be focused on the screen. Furtherdistortion is also encountered because of the projection of a curvedpicture onto a flat screen. I

In Fig. 12 I have illustrated a structure in accordance with theinvention whereby these disadvantages are overcome and at the same timeI am able to completely shield the beam from the 6 glass tube 64. Thefront is slightly larger than the narrowest 8ec-,

second, anode part l8 to the screen upon which the picture isreproduced. The screen 60 is preferably made with an outer layer ofquartz or other similar material 62. On the inner surface of the quartzor Pyrex layer is a layer of phos-v phor or phosphorescent material 68which is then covered by a deposit 01' aluminum 65. Surrrounding thescreen 60, which is preferably circular in shape, is a glass ring 66having a plurality of openings extending therethrough at spacedintervals. A view of this ring 66 is shown in Fig. 14 having theradially spaced openings 61. In this embodiment I have shown a pluralityof longi-, tudinally disposed wires 68 extending from the cylindricalsection l0 oi the tube to the ring 66 with the front or screen ends oithewires 68 being secured in the ring openings 6]. The wires 08 in this"particular embodiment constitute in eiiect extensions of the wires orrods 20 in Fig. 1 or the wires or rods 28 in Figs. 3, 9 and 10. Thewires 88, therefore, are in effect connected to: gether'at the secondanode while being insulated. at the screen part by the glass or quartzring 66. The high voltage connection for energizing the second anode andthe shield wires 68 is made through the connection and the lead "II toonly one of the wires 68. The screen can be similarly polarized by ashort connection .12 from the aluminum layer 65 of the screen to one ofthe wires 68. A substantially-rigid support can be provided for thescreen 60 and the surrounde. ing glass ring 6-6 by providing a pluralityof spaced brackets or springs ll extending outwardly from the ring 66 tocontact the inner surface of the glass envelope 12. In the case of very'highpotentials, the ring 66 itself can be increased in width so as toextend outwardly-and even directly contact and be weldedto the glassenvelope 12.

Fig. 13 is another embodiment of the invention along the lines of thatillustrated in 12.

In this embodiment, however, I have illustrated a structure wh reby Ican get potential gradations between t e screen:60 and the second anodei8 as shown, for instance, in Fig. 3. In

this embodiment the wires 28 are illustrated as.

terminating just inside the flared section of the tube l2 and each ofthe wires is provided with an insulator 80 on its end. A second wire 82extends from the other side of the insulator 20 Similarly, a series ofjumpers 88 are provided between the wires 82 so that each of these wirescan also be maintained at the same potential.

With this arrangement I apply the high voltage potential to the contact10 extending through the wall l2 of the tube which in turn is connectedto the wires 86 by a lead II. A high resistance 90 is connected betweenthe lead II and one of the wires 82. A second resistance 92 is connectedbetween one of the wires 82 and one of the wires 28. The side of theresistor 82 connected with one of the wires 28 is also connected withthe terminal 94 extending through the glass and in turn connected toground 96 through a resistor 88. In this way a voltage divider system isprovided so that it tor instance 100,000 volts are applied at thecontact 10 each or the wires 86 together with the screen will be at thatpotential. The resistors 90, "and 88 may then be proportioned, forexample, so that the potential on the wires 82 will be, say,

75,000 volts and the potential applied to the wires 28 and the secondanode lit-will be about 50,000 volts. The advantages of the employmentof a high voltage on the screen to get added beam acceleration, and,therefore, increased brightness and definition of the image, will berealized while at the same time a materially lower voltage will actuallybe applied to thesecond anode so thata greater degree of safety anddependability will be realized when using thesevided. Since the frontend of the tube is not-in focus when the picture is projected, dirt,smudges,

imperfections in the glass will not appear with objectionable clarity onthe screen and no distortion will be encountered through the formationof a curved picture for projection on the screen.

I claim:

1. In a cathode ray tube a gun structure enclosed within the evacuatedtube envelope com prising means for generating an electron beam,- meansfor controlling and focusing the beam and a second anode foraccelerating the beam including a plurality of individual elongatedconductive elements extending'from said anode in the direction ofmovement of the beam.

2. In a cathode ray tube, a gun structure enclosed within the evacuatedtube envelope comprising means for generating an electron beam, meansfor controlling and focusing the beam and a second anode foraccelerating the beam including a plurality 'of' wire-like elementsextending from the anode in the'direction of movement of the beam, saidelements being spaced about the beam and connected one to the other andto the second anode.

3. In a cathode ray tube according to claim 2 wherein said elementsareelectrically connected together at the second anode and arespaced'substantially uniform y about the beam.

4. In an image reproducing tube, an anode for accelerating the, electronbeam and a plurality of spaced elements each extending from the anode inthe direction of movement of the beam, said elements surrounding andproviding an electrostatic shield for'the beam.

5. In a cathode ray tube wherein the beam is magnetically deflected,means for shielding the electron beam between the accelerating anode andthe screen comprising a plurality of spaced conductors surrounding thebeam and connected together at a point removed from the point ofdeflection of the beam to form a unipotential shield.

6. In a cathode ray tube wherein the beam is magnetically deflected,means for shielding the electron beam between the accelerating anode andthe screen comprising a plurality of spaced conductors surrounding thebeam and connected together at a point removed from the point ofdeflection oi the beam, said conductors being in the form of thin rodsconnected together at the accelerating anode end thereof.

7. An image reproducing tube comprising a cathode for generating anelectron beam, controlling means for said beam including an acceleratinganode, a screen for intercepting said beam, and means for shielding saidbeam comprising a tubular insulator having flared end portions adaptedto contactand be held in position between the anode and the screen bythe reproducing tube wall, and a plurality of wires each fastened at oneend to the anode and extending in spaced relation one to the otherthrough the insulator and bearing firmly against the wall thereof, andmeans for connecting a high accelerating potential to the anode.

JOHN M. CAGE.

REFERENCES CITED UNITED STATES PATENTS Number Name Date Schwartz July12, 1938 Schwartz June 13, 1939 Ruska Oct. '31, 1939 Shoenberg et alNov. 7, 1939 Dillenburger Dec. 2, 1941 Epstein Mar. 3, 1942 Epstein -1July 14, 1942 Gray Aug. 18, 1942

